Waste Isolation Pilot Plant
The Waste Isolation Pilot Plant (WIPP) is an underground repository for low-grade nuclear waste located near Carlsbad, New Mexico. The repository is sited in a natural salt deposit which by its nature, exhibits creep properties. Thus, immediately after an excavation is made, creep in the salt causes the excavation to gradually close over time, completely encapsulating the nuclear waste in salt. The E140 drift is one of the prime access routes from the shaft to the storage area. It is rectangular in shape and was initially supported by rock bolts, mine straps, and chain link wire mesh. Despite this mechanical support, creep of the salt caused a pronounced roof sag. The project required design of a support system to permit use of this drift for a term defined as “long-term, but not permanent”. Because WIPP is an active facility, the long-term support must be installed within the existing large excavation; be installed with minimal interference to ongoing waste disposal operations; and must perform adequately while additional accommodating anticipated time-dependent closure that will occur over the remaining life of the facility. Lachel provided inspection and design services, researched and developed acceptability requirements for several supplemental support options including additional rock bolts, an expansion slot, conventional steel ribs and lagging, continuous corrugated lining, yielding steel arches and lagging. Lachel also researched and developed acceptability requirements for backfill systems including fine and/or course grained salt, fine aggregates (silt/sand/small gravel), course aggregates (sand/gravel), waste rock fragments (caliche, clinker, slag, pumice) polyurethane foam, cellular concrete, and others. This research was then used to provide cost estimates and final recommendations regarding the most appropriate option.